Field of the Invention
One or more embodiments of the present invention generally relate to backlit displays and, more particularly, to reducing power consumption of backlit displays.
Description of the Related Art
Liquid crystal display (LCD) screens, such as the ones used in notebook computers or electronic handheld games, are commonly backlit to make them easier to read. FIG. 1 illustrates an exemplary backlit LCD 100 that includes a core of LCD material 102 between sheets of glass 104 and 106. A backlight source 108 produces light to illuminate the LCD material 102. As illustrated by the arrows, light produced by backlight source 108 is generally diffuse, with components traveling in different directions. The light from backlight source 108 typically passes through a polarizer 110 that blocks light that is not aligned with an axis of polarization of polarizer 110. The light that is aligned with the axis of polarization is allowed to pass through the polarizer 110 to reach the LCD material 102.
The LCD material 102 has electro-optic properties that causes the polarized light that passes through the LCD material 102 to twist. This twisting may be controlled by applying a voltage waveform to the LCD material 102 for each pixel in an array of pixels. Typically, an electronic circuit that controls the array of pixels operates by accepting a digital control value for each pixel in the array of pixels. The control circuit will apply a voltage waveform to the LCD material 102 for a pixel based on the digital control value for the pixel. Generally, the control circuit is configured so that smaller digital control values result in application of a voltage waveform that causes the LCD material 102 to twist the light in such a way that more of the light is blocked by the second polarizer 112, thereby causing the pixel to appear darker. Conversely, larger digital control values result in application of a voltage waveform which causes the LCD material 102 to twist the light in such a way that less of the light is blocked by the second polarizer 112, thereby causing the pixel to appear brighter.
From a power consumption standpoint, conventional LCD backlighting may be far from efficient. Typically, the backlight source 108 illuminates all the pixels in the LCD 100 simultaneously with a relatively constant brightness across all pixels. As previously described, to dim parts of the LCD, a voltage waveform is applied to rows and columns of electrodes supported on the glass substrates 104, 106 that causes the LCD material 102 to twist in a way that results in more of the light generated by the back light source 108 to be blocked. Dimming parts of the LCD in this fashion essentially “wastes” a certain amount of the illumination provided by the backlight source 108 since the backlight source 108 produces the same level of brightness regardless of how much dimming occurs on the screen from the voltage waveform. There are many circumstances where there is a combination of bright and dark images on the screen, and the dark images may be sustained for some period of time. Especially in such situations, the conventional way of illuminating the pixels in the LCD 100 may result in waste. In fact, the power consumption of a backlit LCD may account for a large portion of the overall power consumption of any computer. The inefficiencies due to LCD backlighting may lead to reduced battery life, which may be particularly problematic, for example, when playing video games or viewing DVD movies on long airline flights.
Therefore, a need exists in the art for a method and system for reducing the power consumption of backlit LCD displays.